...
Whatever works for you, I think to have both methods works. I know Jesse and some other people here practice exercises books and cds other than SS. Later as you get better you will start mix and matching excercises. For instance, I will practice using "coo" syllables (something I learned from a John Henny Podcast, he's a level 5 SLS teacher) and even though I am past the "nays" I will still do them from time to time to help me get through my bridges.
Remember as well, Brett started SS because he saw some problems with SLS, he felt that it was incomplete.
Actually I took a sneak peek at some of the more advanced SS lessons, and this is basically how you start to practice, you begin to do lessons on your own and mix and match different vowels and syllables to help you with the lighter or heavier coordination.
I'm not advanced or anything, but being a musician (playing guitar was basically the same thing, you just take different exercises from different people and practice them) I know how to apply all these things. I'm sure Jake or Cuno will have more insight than I.